Project Summary/Abstract: Checkpoint inhibitor therapies provide the ability to treat several previously intractable tumor types; however, only a fraction of patients eligible for the medications respond favorably. Currently patients receiving these treatments must undergo a series of costly imaging sessions to determine their tumor?s response to the medication, yet imaging only provides a static picture of the disease. Health care professionals often wait months before ordering imaging sessions in order to ensure that meaningful tumor growth or recession has occurred according to the iRECIST criteria. The goal of this proposed research is to develop an implantable strain sensor to continuously monitor tumor size throughout the treatment and provide clinicians and cancer researchers with the ability to monitor tumor kinetics. We plan to treat a mouse model for mammary cancer with a combination immunotherapy treatment and use our sensor to continuously detect minute changes in tumor size. We will then look for trends in the data that may provide clues of a positive response, especially within the first 48 hours after treatment when immune cells are known to infiltrate the tumor and cause it to temporarily expand. We hope that this new technology will be used as a method for clinicians to more accurately determine the best time to take a follow up CT scan, and we also believe that this technology could be used to study the relationship between molecular signals and tumor progression. However, in order to develop this type of sensor, we must overcome two fundamental design constraints: the large size associated with power storage and wireless data transfer; and the ability for a sensor to grow and conform to rapidly expanding tissue. Part of the proposed research is to develop a platform technology for transferring power and sensor readings conductively through the body, thereby eliminating the need for a battery and telemetry system and shrinking the device size significantly. We also plan to utilize flexible and stretchable electronic materials developed in our lab to design a device which can expand alongside tissue without exerting any force that could damage the surrounding tissue. We believe that these technologies could be used for a variety of purposes in addition to measuring tumor size and could enable to widespread routine clinical use of implantable biomedical sensors.